Effects ofdirect current on Klebsiella spp. viability and corresponding resistance gene expression in simulative bio-electrochemical reactors

The fate of antibiotic-resistant bacteria (ARB) and associated antibiotic-resistant gene (ARG) expression under electrolytic stimulation in bio-electrochemical reactors (BERs) was unknown. In this study, sulfadiazine resistant bacteria (Klebsiella spp.), which were isolated from a BER, were subjected to constant direct current (DC) stimulation in a simulated BER. With an increase of the current from 7 to 28 mA, it was found that lactic dehydrogenase (LDH) showed a 1.03-, 1.21-, 1.34-, and 1.46-fold value compared with the control at 48 h, indicating that the cell membrane permeability had increased. Since the adenosine triphosphate (ATP) concentration increased with the current, the specific growth rate of Klebsiella spp. increased (R = 0.98). The viable count of Klebsiella spp. reached a maximum at 19 mA and then decreased. The percentage of ARB lethality, which was reflected by flow cytometry analysis, increased from 18% (7 mA) to 37.8% (28 mA) at 48 h. Reactive oxygen species (ROS) produced from the electrolysis of water were greater with the increasing current (R = 0.94), which may be responsible for the high lethality rate of Klebsiella spp.. Scanning electronic microscope results showed that electrolytic stimulation changed the cell surface morphology with some cell disruption. An upregulation of sulII and int1 expression was observed. A significant correlation between int1 and the current (R = 0.97) were observed. Taken together, BERs possess potential risks in accelerating ARB multiplication and promoting ARG expression.